Variable Displacement  Compressor

ABSTRACT

Disclosed is a variable displacement compressor provided with a displacement control valve capable of easily adjusting an optimum level the sensitivity to a rise in the pressure in a crank chamber. The variable displacement compressor is configured in such a manner that the stroke of a piston is adjusted by changing the pressure in the crank chamber, the pressure in the crank chamber being changed by adjusting the degree of opening of the displacement control valve for opening and closing a path for communicating between a discharge chamber and the crank chamber, wherein the displacement control valve is provided with a valve chamber communicating with the discharge chamber, a valve hole, a valve element for opening and closing the valve hole, a pressure sensing chamber communicating with a suction chamber, a pressure sensing member disposed in the pressure sensing chamber, and a pressure sensing rod having one end connected to the pressure sensing member and the other end connected to the valve element and driving the valve element in response to displacement of the pressure sensing member. The pressure in the crank chamber acts on the valve element from the valve hole side in the direction of opening of the valve element, and acts on the pressure sensing rod from the valve hole side in the direction of closing of the valve element. That area (Sr) of the pressure sensing rod which receives the pressure in the crank chamber is set to be greater than that area (Sv) of the valve element which receives the pressure in the crank chamber.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a variable displacement compressor, and specifically, to a variable displacement compressor suitable for use in a refrigeration circuit for an air conditioning system for vehicles.

BACKGROUND ART OF THE INVENTION

A variable displacement compressor is known wherein a displacement control valve for opening and closing a gas supply path communicating between a discharge chamber and a crank chamber by sensing a suction pressure and a throttle disposed in a gas bleeding path communicating between the crank chamber and a suction chamber are provided, the pressure in the crank chamber is varied by adjusting the opening degree of the displacement control valve, thereby adjusting the stroke of the reciprocating motion of pistons, and refrigerant sucked from the suction chamber into cylinder bores is compressed and discharged into a discharge chamber (for example, Patent document 1). Such a variable displacement compressor is provided, for example, in a refrigeration circuit of an air conditioning system for vehicles, and used as a compressor for refrigerant. By introducing refrigerant gas in the discharge chamber into the crank chamber by an amount controlled by the adjustment of opening degree of the displacement control valve while bleeding a small amount of refrigerant gas controlled by a throttle from the crank chamber through the gas bleeding path, the pressure in the crank chamber is controlled at a target pressure, through this control the stroke of pistons is adjusted via control of inclination angle of a swash plate element, and the displacement for discharge of the compressor is controlled at a target displacement.

-   Patent document 1: JP-A-62-282182

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In a variable displacement compressor as described above, although a valve element of the displacement control valve opens and closes the gas supply path in response to displacement of a pressure sensing member (for example, a diaphragm) sensing a suction pressure, because the amount of discharge gas introduced into the crank chamber between a case of a high discharge pressure and a case of a low discharge pressure even if the valve opening degrees are same, in particular, in a case where a throttle disposed in the gas bleeding path communication between the crank chamber and the suction chamber is fixed in opening degree, the sensitivity to a rise in the pressure in the crank chamber (that is, an amount of variation in pressure in a crank chamber relative to an amount of variation in suction pressure) also varies greatly.

In particular, in a case where the discharge pressure is high, because the amount of gas introduced into the crank chamber increases, the sensitivity to a rise in the pressure in the crank chamber tends also to increase. However, if the sensitivity to a rise in the pressure in the crank chamber increases excessively, the displacement for discharge decreases excessively, the above-described operation of the valve element becomes unstable, and there is a case causing a so-called hunting. If such a hunting is caused, for example, in an air conditioning control by an air conditioning system for vehicles using such a variable displacement compressor, a fluctuation in temperature in a vehicle interior may be caused, not only it may give a bad influence to the air conditioning control but also it may cause a fluctuation in torque of the compressor, and in a case where the drive source of the compressor is an engine, it may also give a bad influence to the engine control.

Accordingly, an object of the present invention is to provide a variable displacement compressor provided with a displacement control valve capable of easily adjusting the sensitivity to a rise in the pressure in a crank chamber at an optimum level.

Means for Solving the Problems

To achieve the above object, a variable displacement compressor according to the present invention has a housing in which a discharge chamber, a suction chamber, a crank chamber and cylinder bores are defined therein, pistons inserted into the cylinder bores, a drive shaft supported rotatably in the housing, a motion converting mechanism including a swash plate element capable of being changed with inclination angle for converting a rotation of the drive shaft into a reciprocating motion of the pistons, a displacement control valve for opening and closing a gas supplying path communicating between the discharge chamber and the crank chamber, and a throttle element disposed in a gas bleeding path communicating between the crank chamber and the suction chamber, which adjusts a stroke of the reciprocating motion of the pistons by varying a pressure in the crank chamber by adjusting a degree of opening of the displacement control valve, and which, by the reciprocating motion of the pistons, sucks refrigerant from the suction chamber into the cylinder bores, compresses sucked refrigerant and discharges compressed refrigerant into the discharge chamber, and is characterized in that the displacement control valve is provided with a valve chamber communicating with the discharge chamber, a valve hole having one end communicating with the valve chamber and the other end communicating with the crank chamber, a valve seat formed around the valve hole so as to be confronted to the valve chamber, a valve element disposed in the valve chamber for opening and closing the valve hole by being brought apart from and into contact with the valve seat, a pressure sensing chamber communicating with the suction chamber, a pressure sensing member disposed in the pressure sensing chamber and displaced in response to a pressure in the suction chamber, and a pressure sensing rod having one end connected to the pressure sensing member and the other end connected to the valve element from the valve hole side and driving the valve element in response to displacement of the pressure sensing member; and a pressure in the crank chamber acts on the valve element from the valve hole side in a direction of opening of the valve element, and acts on the pressure sensing rod from the valve hole side in a direction of closing of the valve element, and when a pressure receiving area of the pressure sensing rod which receives a pressure in the crank chamber is represented by “Sr” and a pressure receiving area of the valve element which receives a pressure in the crank chamber is represented by “Sv”, Sr and Sv are set so as to satisfy Sr>Sv.

In such a variable displacement compressor according to the present invention, by setting the pressure receiving area Sr of the pressure sensing rod which receives a pressure in the crank chamber, which acts in the direction of closing of the valve element, greater than the pressure receiving area Sv of the valve element which receives a pressure in the crank chamber, which acts in the direction of opening of the valve element, the pressure in the crank chamber always operates in the direction of closing of the valve element. Since this state where the pressure in the crank chamber always operates in the direction of closing of the valve element basically does not vary even if the discharge pressure varies, it becomes possible to change the sensitivity to a rise in the pressure in the crank chamber (that is, an amount of variation in pressure in a crank chamber relative to an amount of variation in suction pressure) by appropriately adjusting the pressure receiving areas of the respective portions for opening and closing the valve element, and by adequately setting the pressure receiving areas of the respective portions, it becomes possible to stabilize the opening/closing operation of the valve element (that is, a stable operation which does not cause the aforementioned hunting) and to improve the accuracy of the control of the suction pressure. Then, in practice, since the above-described Sr>Sv can be satisfied simply by changing the pressure receiving area of the pressure sensing rod which receives the pressure in the crank chamber without changing other portions, it becomes possible to adjust the sensitivity to a rise in the pressure in the crank chamber extremely easily, and it becomes possible to stabilize the opening/closing state of the valve element and to obtain a stable control state of the displacement for discharge.

In the above-described variable displacement compressor according to the present invention, an embodiment may be employed wherein a pressure in the discharge chamber acts on the valve element in a direction of closing of the valve element, and when a pressure receiving area of the pressure sensing member which receives a pressure in the suction chamber is represented by “Sb”, Sr, Sv and Sb are set so as to satisfy Sb+Sv>2Sr. In such an embodiment, particularly in a case of a structure of displacement control valve where the pressure in the discharge chamber acts in a direction of closing of the valve element, it becomes possible to improve the accuracy of the control of the suction pressure.

Further, in the above-described variable displacement compressor according to the present invention, an embodiment may also be employed wherein the displacement control valve further has a pressure chamber communicating with the suction chamber, the valve element is configured so that one end of the valve element opens and closes the valve hole by being brought apart from and into contact with the valve seat, and the other end of the valve element is disposed in the pressure chamber and a pressure in the suction chamber acts thereon in a direction of closing of the valve element, and when a pressure receiving area of the pressure sensing member which receives a pressure in the suction chamber is represented by “Sb” and a pressure receiving area of the valve element which receives a pressure in the suction chamber is represented by “Sp”, Sr, Sv, Sp and SU are set so as to satisfy Sb+Sp+Sv>2Sr. In such an embodiment, particularly in a case of a structure of displacement control valve where the pressure in the suction chamber acts in a direction of closing of the valve element, it becomes possible to improve the accuracy of the control of the suction pressure.

Moreover, in the above-described latter embodiment, it is preferred that Sp and Sv are set so as to satisfy Sp>Sv. By this, it is suppressed that the valve element opens excessively at the time of decreasing of displacement for discharge, and it becomes possible to further stabilize the opening/closing operation of the valve element.

Furthermore, although the throttle element disposed in the above-described gas bleeding path may be a throttle element capable of adjusting its opening degree, in particular, the present invention is effective in a case where it is an orifice fixed with opening degree. Namely, in the present invention, since, by employing the structure according to the present invention, the sensitivity to a rise in the pressure in the crank chamber can be easily adjusted only by the displacement control valve, in a case where the throttle element disposed in the gas bleeding path communicating between the crank chamber and the suction chamber is an orifice fixed with opening degree, it becomes possible to suppress the sensitivity to a rise in the pressure in the crank chamber to be small particularly when the amount of introduction of discharge gas varies greatly.

The structure of the variable displacement compressor according to the present invention can be applied to any variable displacement compressor which adjusts the stroke of reciprocating motion of pistons by changing the pressure in the crank chamber by the adjustment of opening degree of displacement control valve. In particular, it is suitable to be applied to a case of a compressor provided in a refrigeration circuit for an air conditioning system for vehicles, and since hunting of the valve element of the displacement control valve can be suppressed, the operation of the valve element is stabilized and occurrence of fluctuation of temperature in a vehicle interior can be prevented. Further, because it may be also possible to suppress fluctuation of torque of compressor, in particular, in a case where the drive source for the compressor is an engine, it can also be prevented to give a bad influence to engine control.

Effect According to the Invention

In the variable displacement compressor according to the present invention, by setting the relationship between the pressure receiving area of the pressure sensing rod Sr which receives a pressure in the crank chamber and the pressure receiving area of the valve element Sv which receives a pressure in the crank chamber, in the displacement control valve, at Sr>Sv, it becomes possible to easily adjust the sensitivity to a rise in the pressure in the crank chamber, and to suppress occurrence of hunting, etc. of the valve element and to carry out a target displacement control stably. In particular, it becomes possible to easily adjust the sensitivity to a rise in the pressure in the crank chamber merely by changing the pressure receiving area of the pressure sensing rod which receives a pressure in the crank chamber, the opening/closing operation of the valve element can be stabilized and a stable control state of displacement for discharge can be obtained.

Further, in a case of a structure of displacement control valve where the pressure in the discharge chamber acts in a direction of closing of the valve element, by setting the relationship between the above-described Sr, Sv and the pressure receiving area of the pressure sensing member Sb which receives a pressure in the suction chamber so as to satisfy Sb+Sv>2Sr, the accuracy of the control of the suction pressure can be improved.

Furthermore, in a case of a structure of displacement control valve where the pressure in the suction chamber acts in a direction of closing of the valve element, by setting the relationship between the above-described Sr, Sv, Sb and the pressure receiving area of the valve element Sp which receives a pressure in the suction chamber so as to satisfy Sb+Sp+Sv>2Sr, the accuracy of the control of the suction pressure can be improved. In particular, by setting so as to satisfy Sp>Sv, it is suppressed that the valve element opens excessively at the time of decreasing of displacement for discharge, and it can serve to further stabilize the opening/closing operation of the valve element.

In the present invention, since the sensitivity to a rise in the pressure in the crank chamber can be easily adjusted only by the displacement control valve, the present invention is particularly effective for a case where the throttle element disposed in the gas bleeding path communicating between the crank chamber and the suction chamber is an orifice fixed with opening degree.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of a variable displacement compressor according to a first embodiment of the present invention.

FIG. 2(A) is a vertical sectional view of a displacement control valve in the compressor depicted in FIG. 1, and FIG. 2(B) is an enlarged, partial, vertical sectional view of the displacement control valve.

FIG. 3 depicts diagrams showing the relationships between a suction pressure and a pressure in a crank chamber, which show operations of the displacement control valve depicted in FIG. 2 at respective conditions.

FIG. 4 is a diagram showing the relationship between a discharge pressure and a suction pressure, which shows an example of control property due to the displacement control valve depicted in FIG. 2.

FIG. 5 is a vertical sectional view of a displacement control valve in a variable displacement compressor according to a second embodiment of the present invention.

FIG. 6 is a diagram showing the relationship between an electric current of an electromagnetic coil and a controlled suction pressure, which shows an example of control property due to the displacement control valve depicted in FIG. 5.

EXPLANATION OF SYMBOLS

-   100: variable displacement compressor -   101: cylinder block -   101 a: cylinder bore -   102: front housing -   102 a: boss part -   103: valve plate -   103 a, 103 b: communication hole -   103 c: fixed orifice -   104: rear housing -   104 a: suction port -   104 b: discharge port -   105: crank chamber -   106: drive shaft -   107: swash plate -   108: rotor -   109: connecting part -   110, 111: coil spring -   112: shaft sealing device -   113, 114, 115, 116: bearing -   117: piston -   118: shoe -   119: suction chamber -   120: discharge chamber -   121, 121 a, 121 b: gas supplying path -   122: space -   123: communication path -   200: displacement control valve -   210: valve housing -   210 a, 210 b: valve housing forming member -   211: pressure sensing chamber -   212: communication hole -   213: valve seat -   214: valve hole -   215: communication hole -   216: valve seat -   217: insertion hole -   218: positioning hole -   220: valve element -   230: pressure sensing rod -   240: bellows assembly as pressure sensing member -   241: bellows -   242: end member -   243: guide member -   244: positioning member -   245: compression coil spring -   250: spring -   260: spring guide -   261: communication hole -   270, 271, 272: seal member -   300: displacement control valve -   301: valve housing -   301 a, 301 c, 301 d, 301 e: communication hole -   301 b: valve hole -   302: pressure sensing chamber -   303: bellows assembly -   304: pressure sensing rod -   304 a: valve element -   305: fixed core -   305 a: support hole -   306: valve chamber -   307: movable core -   308: solenoid rod -   309: spring -   310: solenoid case -   311: non-magnetic sleeve -   312: electromagnetic coil -   313: bellows guide -   314: pressure setting member -   315: spring for forcibly opening

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, desirable embodiments of the present invention will be explained referring to figures.

First Embodiment

FIGS. 1-4 show a vertical sectional view of a variable displacement compressor according to a first embodiment of the present invention, a vertical sectional view of a displacement control valve used therefor, and diagrams for explain operations thereof.

(1) Structure of a Variable Displacement Compressor (FIG. 1):

A variable displacement compressor 100 has a cylinder block 101 having a plurality of cylinder bores 101 a, a front housing 102 provided at one end of cylinder block 101, and a rear housing 104 provided at the other end of cylinder block 101 via a valve plate 103, and these form a housing defined in the present invention.

A drive shaft 106 is provided across a crank chamber 105 defined by cylinder block 101 and front housing 102, and around its central portion, a swash plate 107 is disposed. Swash plate 107 is connected to a rotor 108 fixed to drive shaft 106 via a connecting part 109, and the inclination angle thereof can be changed along drive shaft 106. A coil spring 110 is attached between rotor 108 and swash plate 107 for urging swash plate 107 toward the minimum inclination angle side, and a coil spring 111 is attached at the opposite side relative to swash plate 107 for urging swash plate 107 in a direction for increasing the inclination angle.

One end of drive shaft 106 extends up to the outside through the inside of a boss part 102 a of front housing 102 projecting outside, and connected to an electromagnetic clutch which is not shown in the figure. A shaft sealing device 112 is inserted between drive shaft 106 and boss part 102 a, and it seals the inside of the compressor from outside. Drive shaft 106 is supported by bearings 113, 114, 115, 116 in the radial direction and in the thrust direction, and it can be rotated by power transmission through an electromagnetic clutch from an external drive source (for example, an engine for a vehicle).

Each piston 117 is inserted into each cylinder bore 101 a free to reciprocate, the radially outer portion of swash plate 107 is contained in a recessed portion 117 a formed at one end inside piston 117, and piston 117 and swash plate 107 are configured so as to interlock with each other via a pair of shoes 118 sliding on both side surfaces at the radially outer portion of swash plate 107. Therefore, pistons 117 can be reciprocated in cylinder bores 101 a by the rotation of drive shaft 106, and a series of these members form a motion converting mechanism defined in the present invention.

A suction chamber 119 and a discharge chamber 120 are defined in rear housing 104, suction chamber 119 communicates with cylinder bore 101 a via a communication hole 103 a (suction hole) provided on valve plate 103 and a suction valve which is not shown in the figure, and discharge chamber 120 communicates with cylinder bore 101 a via a discharge valve which is not shown in the figure and a communication hole 103 b (discharge hole) provided on valve plate 103. Suction chamber 119 is connected to an air conditioning system side via a suction port 104 a, and discharge chamber 120 is connected to the air conditioning system side via a discharge port 104 b.

A displacement control valve 200 is provided on rear housing 104. Displacement control valve 200 adjusts the opening degree of gas supplying path 121 (121 a, 121 b) communicating between discharge chamber 120 and crank chamber 105, and controls the amount of gas introduced into crank chamber 105. Further, the refrigerant in crank chamber 105 flows into suction chamber 119 through a gas supplying path formed through gaps between the peripheral of drive shaft 106 and bearings 115, 116, a space 122, and a fixed orifice 103 c with a fixed opening degree formed on valve plate 103. Therefore, the pressure in crank chamber 105 can be changed by adjusting the amount of gas discharged into crank chamber 105 by displacement control valve 200, thereby controlling the displacement for discharge.

(2) Structure of Displacement Control Valve (FIG. 2):

As shown in FIG. 2(A), displacement control valve 200 comprises a valve housing 210, a valve element 220, a pressure sensing rod 230, a bellows assembly 240 as a pressure sensing member, a spring 250, a spring guide 260, and seal members 270, 271 and 272.

Valve housing 210 comprises a member 210 a containing bellows assembly 240, and a member 210 b supporting pressure sensing rod 230 slidably and disposed with valve element 220, and the member 210 b is press fitted into the member 210 a. A pressure sensing chamber 211 is defined by member 210 a and member 210 b, and pressure sensing chamber 211 communicates with suction chamber 119 a communication hole 212 and a communication path 123 (FIG. 1).

A valve chamber 213 is formed in member 212 b, one side of valve chamber 213 communicates with discharge chamber 120 through a communication hole formed on spring guide 260 and gas supplying path 121 a, and the other side of valve chamber 213 communicates with crank chamber 105 through a communication hole 215 and gas supplying path 121 b.

Valve element 220 is disposed in valve chamber 213, and valve element 220 opens and closes a valve hole 214 by being brought apart from and into contact with a valve seat 216. One end of spring 250 comes into contact with valve element 220, and the other end comes into contact with spring guide 260, and valve element 220 is urged in the valve opening direction by the urging force of spring 250. Spring guide 260 is press fitted in the circumferential wall of valve chamber 213.

An insertion hole 217 for supporting pressure sensing rod 230 slidably is formed in member 210 b, the gap between the outer circumference of pressure sensing rod 230 and insertion hole 217 is set very small, and pressure sensing chamber 211 and valve hole 214 are separated from each other at an almost gas-tight condition.

As shown in FIG. 2(B), bellows assembly 240 comprises a bellows 241, an end member 242 closing both ends of bellows 241, a guide member 243 receiving one end of pressure sensing rod 230, a positioning member 244 positioned by member 210 a, and a compression coil spring 245 disposed in bellows 241 and urging bellows assembly 240 in its expanding direction. The inside of this bellows assembly 240 is kept at a substantially vacuum condition.

Bellows assembly 240 is disposed in pressure sensing chamber 211, and positioning member 244 is fitted into and fixed to a positioning hole 218 formed in member 210 a. Further, since guide member 243 receives one end of pressure sensing rod 230 and the other end of pressure sensing rod 230 comes into contact with valve element 220 from valve hole 214 side, valve element 220 opens and closes valve hole 214 in response to expansion and contraction of bellows assembly 240.

Seal member 270 ensures the gas tight condition between the atmospheric side and the region operated with the pressure in suction chamber 119, seal member 271 ensures the gas tight condition between the region operated with the pressure in suction chamber 119 and the region operated with the pressure in crank chamber 105, and seal member 272 ensures the gas tight condition between the region operated with the pressure in crank chamber 105 and the region operated with the pressure in discharge chamber 120

(3) Property of Displacement Control Valve:

On valve element 220, the pressure in discharge chamber 120 (hereinafter, referred to as discharge pressure Pd) acts in a direction of valve closing and the pressure in crank chamber 105 (hereinafter, referred to as pressure in crank chamber Pc) in a direction of valve opening, and on pressure sensing rod 230, the pressure in crank chamber Pc acts in a direction of valve closing and the pressure in suction chamber 119 (hereinafter, referred to as suction pressure Ps) acts in a direction of valve opening. Further, the suction pressure Ps acts on bellows assembly 240 in a direction of valve closing.

Where, because valve seat 216 forms an edge portion of the opening end of valve hole 214, the pressure receiving area Sv of the pressure in crank chamber Pc acting on valve element 220 is nearly equal to the cross sectional area of valve hole 214. Further, the pressure receiving area Sr of the pressure in crank chamber Pc acting on pressure sensing rod 230 is the cross sectional area of the pressure sensing rod 230 located in the region supported by insertion hole 217, and set is Sr>Sv. By this, the pressure in crank chamber Pc always acts in a direction closing valve element 220. When the pressure receiving area (effective area) for receiving the suction pressure Ps which acts in a direction of the expansion and contraction of bellows assembly 240 is represented by Sb, the urging force of spring 250 is represented by fs and the urging force of bellows assembly 240 is represented by Fb, the force acting on valve element 220 is represented by the following equation [Equation 1] (including equations (1) and (2)).

[Equation 1]

fs+(Pd−Pc)·Sv+Pc·Sr+Ps·(Sb−Sr)−Fb=0  (1)

Pc=−[(Sb−Sr)/(Sr−Sv)]·Ps−[Sv/(Sr−Sv)]·Pd+(Fb−fs)/(Sr−Sv)  (2)

The meanings represented by the respective signs in the above-described [Equation 1] are as follows.

Ps: suction pressure Pc: pressure in crank chamber Pd: discharge pressure Sv: pressure receiving area of pressure in crank chamber acting on valve element Sr: pressure receiving area of pressure in crank chamber acting on pressure sensing rod Sb: pressure receiving area of suction pressure acting in direction of expansion and contraction of bellows (effective area) fs: urging force of spring 250 Fb: urging force of bellows assembly 240

In the equation (2) of the above-described [Equation 1], in case where Pd is referred to be constant, Pc becomes a linear function of Ps, Pc has a characteristic such that Pc decreases when Ps increases and Pc increases on the contrary when Ps decreases, and the gradient thereof is determined by (Sb−Sr)/(Sr−Sv). Namely, the coefficient of Ps “(Sb−Sr)/(Sr−Sv)” is a sensitivity of variation of Pc relative to variation of Ps.

For example, as shown in FIGS. 3 (A) to (C), depending upon the level of (Sb−Sr)/(Sr−Sv), the sensitivity of the pressure in crank chamber Pc varies when the suction pressure Ps varies. Since Sb, Sv and Sr are pressure receiving areas of the respective pressures, by adjusting the respective pressure receiving areas, it becomes possible to adjust the sensitivity of the pressure in crank chamber Pc when the suction pressure Ps varies.

Where, if (Sb−Sr)/(Sr−Sv)=1 is satisfied, namely, if Sb+Sv=2Sr is satisfied, the amount of variation of the suction pressure Ps is equal to the amount of variation of the pressure in crank chamber Pc, if (Sb−Sr)/(Sr−Sv)>1 is satisfied, the amount of variation of the pressure in crank chamber Pc relative to the amount of variation of the suction pressure Ps increases, and if (Sb−Sr)/(Sr−Sv)<1 is satisfied, the amount of variation of the pressure in crank chamber Pc relative to the amount of variation of the suction pressure Ps decreases.

Therefore, if Sb, Sr and Sv are set so as to satisfy (Sb−Sr)/(Sr−Sv)>1, that is, Sb+Sv>2Sr, the suction pressure Ps can be controlled at a high accuracy.

Thus, if Sr>Sv is satisfied, the pressure in crank chamber Pc acts in a direction closing valve element 220, and as a result, as shown in [Equation 1], it becomes possible to change the sensitivity of the pressure in crank chamber Pc, at the time when the suction pressure Ps varies, by adequately adjusting Sb, Sr and Sv, and the state of opening/closing of valve element 220 may be stabilized and the control accuracy of the suction pressure may be improved.

Where, although Pd=constant is employed in the above-described explanation, from equation (2), when Pc is referred to be a linear function of Ps, Pd is merely a parameter, and therefore, even if Pd varies, the above-described explanation does not change. Namely, by setting Sr>Sv, the above-described operation and advantage can be obtained.

(4) Operation for Displacement Control of Variable Displacement Compressor:

When equation (2) is transformed, it becomes equation (3) (the following [Equation 2]). Equation (3) shows the control property of suction pressure of displacement control valve 200, and as shown in FIG. 4, the property is set such that, when the discharge pressure Pd increases, the suction pressure Ps is amended so as to be slightly decreased.

[Equation 2]

Ps=−[Sv/(Sb−Sr)]·Pd−[(Sr−Sv)/(Sb−Sr)]·Pc+(Fb−fs)/(Sb−Sr)  (3)

In a state where variable displacement compressor 100 does not operate, the refrigerant pressure is balanced, and for example, if the outside air temperature is high, the suction pressure Ps is remarkably higher than equation (3). In this case, bellows assembly 240 is contracted by the force of the suction pressure Ps, and by this, valve element 220 closes valve hole 214.

From this state, when variable displacement compressor 100 is activated, because discharge gas is not introduced into crank chamber 105, the refrigerant gas (blow-by gas) in crank chamber 105 flows out into suction chamber 119 through the gas bleeding path, the pressure in crank chamber Pc becomes equal to the suction pressure Ps, and as a result, the inclination angle of swash plate 107 increases and the piston stroke is maintained at maximum.

When the suction pressure Ps gradually decreases by the operation of variable displacement compressor 100, bellows assembly 240 expands, and when the suction pressure Ps reaches the property of equation (3), pressure sensing rod 230 pushes up valve element 220 and valve hole 214 is opened, and as a result, the discharge gas is introduced into crank chamber 105.

Since the refrigerant gas flowing out from crank chamber 105 into suction chamber 119 is restricted by fixed orifice 103 c in the gas bleeding path, the pressure in crank chamber Pc increases, and by this, the inclination angle of swash plate 107 decreases and the piston stroke decreases.

Where, the degree of increase of the pressure in crank chamber Pc, that is, the amount of variation of the pressure in crank chamber Pc relative to the amount of variation of the suction pressure Ps is adequately adjusted by setting of Sb, Sr and Sv (Sb+Sv>2Sr).

Although the suction pressure Ps is likely to increase when the piston stroke decreases, if the suction pressure Ps increases, because bellows assembly 240 is likely to be contracted, valve element 220 is displaced in a direction of valve closing. By this, the amount of discharge gas introduced into crank chamber 105 decreases, the pressure in crank chamber Pc decreases, and therefore, the decrease of piston stroke is stopped, and valve element 220 is maintained at a predetermined opening degree.

If the suction pressure Ps decreases ascribed to any external disturbance, bellows assembly 240 again expands and pushes up valve element 220, the amount of discharge gas introduced into crank chamber 105 is increased and the pressure in crank chamber Pc increases, and by this, the inclination angle of swash plate 107 decreases and the piston stroke decreases.

By such an operation, the piston stroke is controlled so that the suction pressure Ps approaches the control property of suction pressure of the above-described equation (3).

Thus, in the present invention, as is understood from the above-described equation (2), merely by changing only the sectional area Sr of pressure sensing rod 230, the amount of variation of the pressure in crank chamber Pc relative to the amount of variation of the suction pressure Ps can be changed. Therefore, even if are not changed in design main elements concerning the basic structure of a displacement control valve such as the sectional area Sv of valve hole 214 affecting the property of flow rate or the pressure receiving area (effective area) Sb of the suction pressure acting in a direction for expanding and contracting bellows assembly 240, the amount of variation of the pressure in crank chamber Pc relative to the amount of variation of the suction pressure Ps can be changed, and the sensitivity to a rise of the pressure in crank chamber of the displacement control valve may be easily optimized in accordance with various variable displacement compressors. By this, even in case where various specifications are required for displacement control valves, main elements of the displacement control valves may be designed in common.

Second Embodiment

FIG. 5 shows a displacement control valve 300 according to a second embodiment of the present invention.

In this second embodiment, parts basically different from the aforementioned first embodiment are that, although in displacement control valve 200 shown in FIG. 2 the discharge pressure Pd operates in a direction for closing the valve element, in displacement control valve 300 shown in FIG. 5 the suction pressure Ps operates in a direction for closing the valve element and the discharge pressure Pd does not act on the valve element, and that it is a so-called external control type displacement control valve in which an electromagnetic force is operated on the valve element.

Structure of Displacement Control Valve:

Referring to FIG. 5, displacement control valve 300 comprises a bellows assembly 303 functioning as a pressure sensing member which is disposed in a pressure sensing chamber 302 formed in a valve housing 301 and receives the suction pressure through a communication hole 301 a and a communication path 123 and in which a spring is disposed in its vacuum inside, a pressure sensing rod 304 whose one end is brought into contact with this bellows assembly 303 and which is supported slidably in valve housing 301, a valve element 304 a which is formed being integrated with this pressure sensing rod 304 the other end of which is supported slidably in a support hole 305 a of fixed core 305, which is disposed in valve chamber 306 and which opens and closes a valve hole 301 b in response to expansion and contraction of bellows assembly 303, a solenoid rod 308 whose one end surface is brought into contact with the other end surface of valve element 304 a and to the other end of which a movable core 307 disposed confronting a fixed core 305 with a predetermined gap is fixed, a spring 309 urging movable core 307 in a valve closing direction of valve closing, a non-magnetic sleeve 311 supporting the outer circumference of movable core 307 slidably into which fixed core 305 is inserted and which is fixed to a solenoid case 310, and a coil 312 which is disposed on the outer circumference of sleeve 311 and which generates an electromagnetic force. Where, the solenoid comprises solenoid rod 308, sleeve 311, solenoid case 310 and electromagnetic coil 312.

Further, the end of bellows assembly 303 at a side opposite to pressure sensing rod 304 is supported by a bellows guide 313, and this bellows guide 313 is supported slidably by a pressure setting member 314. Further, a spring for forcibly opening 315 for urging bellows assembly 303 in a direction of valve opening is disposed between pressure setting member 314 and bellows guide 313. Pressure setting member 314 is press fitted into valve housing 301 so that displacement control valve 300 becomes a predetermined pressure setting.

Valve chamber 306 communicates with discharge chamber 120 through communication hole 301 c. Valve hole 301 b communicates with crank chamber 105 through communication hole 301 d. Therefore, communication hole 301 c, valve chamber 306, valve hole 301 b and communication hole 301 d form a part of gas supplying path 121.

The space in sleeve 311 disposed with movable core 307, solenoid rod 8 and the other end surface of valve element 304 a communicates with pressure sensing chamber 302 through communication hole 301 e. Therefore, the pressure in crank chamber Pc acts on one end surface of valve element 304 a (surface at the side of valve hole 301 b), and the suction pressure Pc acts on the other end surface of valve element 304 a.

Since the sectional area Sp of valve element 304 a supported in support hole 305 a is set slightly greater than the sectional area Sv of valve hole 301 b, the force of the discharge pressure Pd in valve chamber 306 slightly acts in a direction for opening valve element 304 a. Further, the sectional area Sr of pressure sensing rod 304 is set greater than the sectional area Sv of valve hole 301 b, and the pressure in crank chamber Pc acts in a direction for closing the valve element.

Therefore, the force operating on valve element 304 a of displacement control valve 300 can be represented by the following equations [Equation 3] (including equations (4) and (5)).

[Equation 3]

F(I)+fs1+Ps·Sp−Pc·Sv−(Sp−Sv)·Pd+Pc·Sr+Ps·(Sb−Sr)−Fb−fs2=0  (4)

Pc=−[(Sb+Sp−Sr)/(Sr−Sv)]·Ps+[(Sp−Sv)/(Sr−Sv)]Pd+[(Fb−fs1+fs2−F(I))/(Sr−Sv)]  (5)

(Sb>Sr>Sv, Sp>Sv)

The meanings represented by the respective signs in the above-described [Equation 3] are as follows.

Ps: suction pressure Pc: pressure in crank chamber Pd: discharge pressure Sv: pressure receiving area of pressure in crank chamber acting on valve element Sp: pressure receiving area of suction pressure acting on valve element Sr: pressure receiving area of pressure in crank chamber acting on pressure sensing rod Sb: pressure receiving area of suction pressure acting in direction of expansion and contraction of bellows (effective area) fs1: urging force of spring 309 fs2: urging force of spring 315 Fb: urging force of bellows assembly 303 F(I): electromagnetic force of solenoid

In the above-described equation (5), in case where Pd and F(I) are referred to be constant, Pc becomes a linear function of Ps, Pc has a characteristic such that Pc decreases when Ps increases and Pc increases on the contrary when Ps decreases, and the gradient thereof is determined by (Sb+Sp−Sr)/(Sr−Sv). Namely, the coefficient of Ps “(Sb+Sp−Sr)/(Sr−Sv)” is a sensitivity of variation of Pc relative to variation of Ps.

Because Sb, Sv, Sp and Sr are pressure receiving areas of the respective pressures, the sensitivity of the pressure in crank chamber Pc at the time when the suction pressure Ps varies can be adjusted by adjusting the respective pressure receiving areas.

Where, if (Sb+Sp−Sr)/(Sr−Sv)=1 is satisfied, namely, if Sb+Sp+Sv=2Sr is satisfied, the amount of variation of the suction pressure Ps is equal to the amount of variation of the pressure in crank chamber Pc, if (Sb+Sp−Sr)/(Sr−Sv)>1 is satisfied, the amount of variation of the pressure in crank chamber Pc relative to the amount of variation of the suction pressure Ps increases, and if (Sb+Sp−Sr)/(Sr−Sv)<1 is satisfied, the amount of variation of the pressure in crank chamber Pc relative to the amount of variation of the suction pressure Ps decreases. Therefore, if Sb, Sp, Sr and Sv are set so as to satisfy (Sb+Sp−Sr)/(Sr−Sv)>1, that is, Sb+Sp+Sv>2Sr, the suction pressure Ps can be controlled at a high accuracy.

Thus, if Sr>Sv is satisfied, the pressure in crank chamber Pc acts in a direction closing valve element 304 a, and as a result, as shown in [Equation 3], it becomes possible to change the sensitivity of the pressure in crank chamber Pc, at the time when the suction pressure Ps varies, by adequately adjusting Sb, Sp, Sr and Sv, and the state of opening/closing of valve element 304 a may be stabilized and the control accuracy of the suction pressure may be improved.

Further, in displacement control valve 300, Sp is set slightly greater than Sv. For example, if the opening degree of valve element 304 a increases and the pressure in crank chamber Pc increases, the displacement for discharge decreases, but accompanying with the decrease of the displacement for discharge, the discharge pressure Pd is to be decreased. If it is set so that Sp>Sv is satisfied and the discharge Pd acts in a direction of valve opening, when the displacement for discharge decreases, because the force in a direction of valve opening due to the discharge pressure Pd, which acts on valve element 304 a, decreases, it is effective to suppress an excessive opening of valve element 304 a, and it contributes to stabilize the opening/closing state of valve element 304 a.

Although Pd and F(I) are constant in the above-described explanation, from the above-described equation (5), when Pc is referred to be a linear function of Ps, Pd and F(I) are merely parameters, and therefore, even if Pd and F(I) vary, the above-described explanation does not change.

Where, when the above-described equation (5) is transformed, equation (6) can be obtained (the following [Equation 4]). Equation (6) shows the control property of suction pressure of displacement control valve 300, and as shown in FIG. 6, the property is set such that, as the current of the solenoid (electromagnetic coil) increases, the controlled suction pressure is decreased.

[Equation 4]

Ps=−[1/(Sb+Sp−Sr)]·F(I)+[(Sp−Sv)/(Sb+Sp−Sr)]·Pd−[(Sr−Sv)/(Sb+Sp−Sr)]·Pc+[(Fb−fs1+fs2)/(Sb+Sp−Sr)]  (6)

In the above-described respective embodiments, although the inside of the bellows assembly is set at a vacuum pressure, the inside of the bellows assembly may be set at an atmospheric pressure. Further, as the pressure sensing member, a diaphragm may be employed. Further, although the displacement control valve shown in FIG. 2 is a mechanical control valve, it may be formed as an external control type displacement control valve by adding a solenoid so as to operate an electromagnetic force to a valve element. Furthermore, although Sp>Sv is set in the displacement control valve shown in FIG. 5, Sp=Sv or Sp<Sv may be set.

Moreover, the present invention may be applied to a wabble type variable displacement compressor or a variable displacement compressor driven by a motor, and may be applied to any of a variable displacement compressor equipped with an electromagnetic clutch and a clutch-less compressor. Further, as the throttle element provided in the gas bleeding path, except the above-described orifice with a fixed opening degree, a throttle capable of being varied with flow rate, or a structure in which opening/closing control is carried out by a valve element, can also be employed.

Furthermore, the present invention can be applied to a variable displacement compressor using a new refrigerant (for example, refrigerant recently reported for preventing global warming) instead of the present refrigerant R134 a.

INDUSTRIAL APPLICATIONS OF THE INVENTION

The present invention can be applied to any variable displacement compressor which adjusts the stroke of pistons by changing the pressure in the crank chamber by the adjustment of opening degree of displacement control valve, and in particular, it is suitable as a variable displacement compressor provided in a refrigeration circuit for an air conditioning system for vehicles. 

1. A variable displacement compressor having a housing in which a discharge chamber, a suction chamber, a crank chamber and cylinder bores are defined therein, pistons inserted into said cylinder bores, a drive shaft supported rotatably in said housing, a motion converting mechanism including a swash plate element capable of being changed with inclination angle for converting a rotation of said drive shaft into a reciprocating motion of said pistons, a displacement control valve for opening and closing a gas supplying path communicating between said discharge chamber and said crank chamber, and a throttle element disposed in a gas bleeding path communicating between said crank chamber and said suction chamber, which adjusts a stroke of said reciprocating motion of said pistons by varying a pressure in said crank chamber by adjusting a degree of opening of said displacement control valve, and which, by said reciprocating motion of said pistons, sucks refrigerant from said suction chamber into said cylinder bores, compresses sucked refrigerant and discharges compressed refrigerant into said discharge chamber, characterized in that: said displacement control valve is provided with a valve chamber communicating with said discharge chamber, a valve hole having one end communicating with said valve chamber and the other end communicating with said crank chamber, a valve seat formed around said valve hole so as to be confronted to said valve chamber, a valve element disposed in said valve chamber for opening and closing said valve hole by being brought apart from and into contact with said valve seat, a pressure sensing chamber communicating with said suction chamber, a pressure sensing member disposed in said pressure sensing chamber and displaced in response to a pressure in said suction chamber, and a pressure sensing rod having one end connected to said pressure sensing member and the other end connected to said valve element from said valve hole side and driving said valve element in response to displacement of said pressure sensing member; and a pressure in said crank chamber acts on said valve element from said valve hole side in a direction of opening of said valve element, and acts on said pressure sensing rod from said valve hole side in a direction of closing of said valve element, and when a pressure receiving area of said pressure sensing rod which receives a pressure in said crank chamber is represented by “Sr” and a pressure receiving area of said valve element which receives a pressure in said crank chamber is represented by “Sv”, Sr and Sv are set so as to satisfy Sr>Sv.
 2. The variable displacement compressor according to claim 1, wherein a pressure in said discharge chamber acts on said valve element in a direction of closing of said valve element, and when a pressure receiving area of said pressure sensing member which receives a pressure in said suction chamber is represented by “Sb”, Sr, Sv and Sb are set so as to satisfy Sb+Sv>2Sr.
 3. The variable displacement compressor according to claim 1, wherein said displacement control valve further has a pressure chamber communicating with said suction chamber, said valve element is configured so that one end of said valve element opens and closes said valve hole by being brought apart from and into contact with said valve seat, and the other end of said valve element is disposed in said pressure chamber and a pressure in said suction chamber acts thereon in a direction of closing of said valve element, and when a pressure receiving area of said pressure sensing member which receives a pressure in said suction chamber is represented by “Sb” and a pressure receiving area of said valve element which receives a pressure in said suction chamber is represented by “Sp”, Sr, Sv, Sp and Sb are set so as to satisfy Sb+Sp+Sv>2Sr.
 4. The variable displacement compressor according to claim 3, wherein Sp and Sv are set so as to satisfy Sp>Sv.
 5. The variable displacement compressor according to claim 1, wherein said throttle element disposed in said gas bleeding path is an orifice fixed with opening degree.
 6. The variable displacement compressor according to claim 1, wherein said variable displacement compressor is a compressor provided in a refrigeration circuit for an air conditioning system for vehicles. 